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c9cf6dde | 1 | /* Startup code compliant to the ELF x86-64 ABI. |
f7a9f785 | 2 | Copyright (C) 2001-2016 Free Software Foundation, Inc. |
c9cf6dde AJ |
3 | This file is part of the GNU C Library. |
4 | Contributed by Andreas Jaeger <aj@suse.de>, 2001. | |
5 | ||
6 | The GNU C Library is free software; you can redistribute it and/or | |
7 | modify it under the terms of the GNU Lesser General Public | |
8 | License as published by the Free Software Foundation; either | |
9 | version 2.1 of the License, or (at your option) any later version. | |
10 | ||
92c6ccd1 RM |
11 | In addition to the permissions in the GNU Lesser General Public |
12 | License, the Free Software Foundation gives you unlimited | |
13 | permission to link the compiled version of this file with other | |
14 | programs, and to distribute those programs without any restriction | |
15 | coming from the use of this file. (The GNU Lesser General Public | |
16 | License restrictions do apply in other respects; for example, they | |
17 | cover modification of the file, and distribution when not linked | |
18 | into another program.) | |
19 | ||
20 | Note that people who make modified versions of this file are not | |
21 | obligated to grant this special exception for their modified | |
22 | versions; it is their choice whether to do so. The GNU Lesser | |
23 | General Public License gives permission to release a modified | |
24 | version without this exception; this exception also makes it | |
25 | possible to release a modified version which carries forward this | |
26 | exception. | |
27 | ||
c9cf6dde AJ |
28 | The GNU C Library is distributed in the hope that it will be useful, |
29 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
30 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
31 | Lesser General Public License for more details. | |
32 | ||
33 | You should have received a copy of the GNU Lesser General Public | |
59ba27a6 PE |
34 | License along with the GNU C Library; if not, see |
35 | <http://www.gnu.org/licenses/>. */ | |
c9cf6dde AJ |
36 | |
37 | /* This is the canonical entry point, usually the first thing in the text | |
38 | segment. The SVR4/i386 ABI (pages 3-31, 3-32) says that when the entry | |
39 | point runs, most registers' values are unspecified, except for: | |
40 | ||
41 | %rdx Contains a function pointer to be registered with `atexit'. | |
42 | This is how the dynamic linker arranges to have DT_FINI | |
43 | functions called for shared libraries that have been loaded | |
44 | before this code runs. | |
45 | ||
46 | %rsp The stack contains the arguments and environment: | |
6cdef1ab L |
47 | 0(%rsp) argc |
48 | LP_SIZE(%rsp) argv[0] | |
c9cf6dde | 49 | ... |
6cdef1ab L |
50 | (LP_SIZE*argc)(%rsp) NULL |
51 | (LP_SIZE*(argc+1))(%rsp) envp[0] | |
c9cf6dde | 52 | ... |
6cdef1ab | 53 | NULL |
c9cf6dde AJ |
54 | */ |
55 | ||
6a1bd2a1 | 56 | #include <sysdep.h> |
c9cf6dde | 57 | |
467fec0b | 58 | ENTRY (_start) |
6a1bd2a1 JK |
59 | /* Clearing frame pointer is insufficient, use CFI. */ |
60 | cfi_undefined (rip) | |
c9cf6dde AJ |
61 | /* Clear the frame pointer. The ABI suggests this be done, to mark |
62 | the outermost frame obviously. */ | |
ee618985 | 63 | xorl %ebp, %ebp |
c9cf6dde AJ |
64 | |
65 | /* Extract the arguments as encoded on the stack and set up | |
66 | the arguments for __libc_start_main (int (*main) (int, char **, char **), | |
67 | int argc, char *argv, | |
68 | void (*init) (void), void (*fini) (void), | |
69 | void (*rtld_fini) (void), void *stack_end). | |
70 | The arguments are passed via registers and on the stack: | |
71 | main: %rdi | |
72 | argc: %rsi | |
73 | argv: %rdx | |
74 | init: %rcx | |
75 | fini: %r8 | |
76 | rtld_fini: %r9 | |
77 | stack_end: stack. */ | |
78 | ||
6cdef1ab | 79 | mov %RDX_LP, %R9_LP /* Address of the shared library termination |
c9cf6dde | 80 | function. */ |
6cdef1ab L |
81 | #ifdef __ILP32__ |
82 | mov (%rsp), %esi /* Simulate popping 4-byte argument count. */ | |
83 | add $4, %esp | |
84 | #else | |
c9cf6dde | 85 | popq %rsi /* Pop the argument count. */ |
6cdef1ab L |
86 | #endif |
87 | /* argv starts just at the current stack top. */ | |
88 | mov %RSP_LP, %RDX_LP | |
c9cf6dde | 89 | /* Align the stack to a 16 byte boundary to follow the ABI. */ |
6cdef1ab | 90 | and $~15, %RSP_LP |
c9cf6dde | 91 | |
6cdef1ab L |
92 | /* Push garbage because we push 8 more bytes. */ |
93 | pushq %rax | |
c9cf6dde AJ |
94 | |
95 | /* Provide the highest stack address to the user code (for stacks | |
96 | which grow downwards). */ | |
97 | pushq %rsp | |
98 | ||
d49c05e0 UD |
99 | #ifdef SHARED |
100 | /* Pass address of our own entry points to .fini and .init. */ | |
6cdef1ab L |
101 | mov __libc_csu_fini@GOTPCREL(%rip), %R8_LP |
102 | mov __libc_csu_init@GOTPCREL(%rip), %RCX_LP | |
d49c05e0 | 103 | |
29691210 | 104 | mov main@GOTPCREL(%rip), %RDI_LP |
d49c05e0 UD |
105 | |
106 | /* Call the user's main function, and exit with its value. | |
107 | But let the libc call main. */ | |
29691210 | 108 | call __libc_start_main@PLT |
d49c05e0 | 109 | #else |
c9cf6dde | 110 | /* Pass address of our own entry points to .fini and .init. */ |
6cdef1ab L |
111 | mov $__libc_csu_fini, %R8_LP |
112 | mov $__libc_csu_init, %RCX_LP | |
c9cf6dde | 113 | |
29691210 | 114 | mov $main, %RDI_LP |
c9cf6dde AJ |
115 | |
116 | /* Call the user's main function, and exit with its value. | |
117 | But let the libc call main. */ | |
29691210 | 118 | call __libc_start_main |
d49c05e0 | 119 | #endif |
c9cf6dde AJ |
120 | |
121 | hlt /* Crash if somehow `exit' does return. */ | |
467fec0b | 122 | END (_start) |
c9cf6dde AJ |
123 | |
124 | /* Define a symbol for the first piece of initialized data. */ | |
125 | .data | |
126 | .globl __data_start | |
127 | __data_start: | |
128 | .long 0 | |
129 | .weak data_start | |
130 | data_start = __data_start |